The 90 degree type, with the elbows on the pads, give better leverage and focus on the pec's themselves.
The type where the arms/hands are extended further from the body (tree hugger) transfer a lot of the resistance on the out stretched handles/arms/elbows and even shoulder joints. Which in return lessens the direct influence on the pec's.
Going to use much more weight on the 90 degree, elbows on pad pec deck style. It also works better when doing reverse rear delt work (arms will be crossed in front of the body to start). Doing both versions, in the same work out, might be interesting. Probably get a great pump, though a pump does not always mean muscle growth. But the more effective version would be the 90 degree machine, by far. Some find this version can also help their BP, which is only logical. Good Luck.